Recipe10.10.Troubleshooting Network Connectivity Problems

Recipe 10.10. Troubleshooting Network Connectivity Problems

Problem

You want to troubleshoot network connectivity problems. This is often necessary if a client is experiencing slow logins or network-based failures when accessing resources.

Solution

First, make sure your network adapter is working. Generally there should be a flashing green light to indicate the adapter is connected and transmitting data.

After you've checked the hardware, you can run several command-line tools to aid in troubleshooting connectivity issues. A good first step is to ping the target host, which can tell you if the remote host is reachable and how long it takes to reach it:

> ping <HostNameOrIP>

Here are some of the status messages you can receive from ping:

Reply: The host was reachable.
Request timed out: The target host either did not respond or there is no host configured with the corresponding IP address. You may also see this message if there is a lot of network latency between the two endpoints. You can work around this by using the -w option with ping and specifying the number of milliseconds to wait for each reply.
Unknown host: If you used a DNS name in the ping command, this indicates that the DNS name was not resolvable by the DNS client.
Destination unreachable: The ICMP traffic could not reach the network of the target host. This is often due to a routing problem on an intermediate router or a router being down.

If you've pinged a host and the request timed out or the host was unreachable, a good tool to try next is tracert, which attempts to trace a route from the source computer to the destination computer.

> tracert <HostNameOrIP>

This command shows you the path your data takes to get to the destination. If there are connectivity problems with a remote host, this command shows where the problem occurs.

If everything checks out, next run the netdiag command on the target system. netdiag provides a wealth of information about various network settings configured on the system along with information about DNS, Kerberos, and Active Directory connectivity. Use the /debug option to view detailed output. If you suspect authentication (Kerberos) to be a potential issue, run the kerbtray utility to ensure you have functioning Kerberos tickets.

If you are still having network problems, a good last step is to look at the network traffic to see if you can spot any obvious errors being transmitted. See Recipe 10.11 for more information.